Raman spectroscopy has proven to be a highly valuable portable analytical tool for accurate chemical identifications. In the most common implementation, a Raman spectrometer requires the operator to hold the device close (e.g., less than couple of centimeters away) to the substance under investigation, illuminating the substance with a pump laser and collecting the Raman scattering. With typical portable Raman instruments, the laser hazard zone is half a meter or larger and laser training is required for the operators of such a tool since it is typically classified as a Class 3B instrument. Standoff Raman systems with a meter or more of standoff distance from sample also exist but the laser hazard zone is much larger (e.g., a few meters) preventing easy adoption of such systems in the field in addition to burdening the operators and manufacturers with a more onerous laser safety training class.
For visible or near-infrared (NIR) Raman systems laser hazard is due to ocular damage, in particular thermal damage to the retina, from the laser used as the Raman pump. The damage is a function of radiance (W/m2/sr), distance of Raman laser source to the eye, wavelength, and exposure time. For a standoff Raman system, the laser power exits the system output aperture and converges to a spot outside the system, on a target sample.